Adhesive composition and uses thereof

ABSTRACT

Disclosed herein is an adhesive composition for clutch disc application comprising of an epoxy resin of bisphenol A and epichlotrohydrin, partially hydrogenated carboxylated nitrile butadiene rubber (HX-NBR) in solid form as a toughening agent in the ratio 80:20, and optionally with additives to obtain improved lap shear strength and cushioning properties.

FIELD OF THE INVENTION

The present invention relates to an adhesive composition to obtain improved lap shear strength and cushioning property for clutch applications.

Particularly, the present invention further relates to adhesive composition comprising an epoxy resin in the range of 50-95 parts by weight and an elastomer in the range of 2 to 50 parts by weight and optionally a toughening agent in the range of 2-50 parts by weight and also optionally one or more additives in the range of 2-5 parts by weight.

BACKGROUND AND PRIOR ART OF THE INVENTION

A clutch in an automobile contains frictional material on a SS or MS plate/sheet. A clutch disc moves to and fro, it is engaged while moving and while disengaged, it is stationary. The friction material used in clutches is very expensive and is attached to the SS plate mechanically with rivets. But these rivets prevent the entire material from wearing off (entire material should be worn off, if not, material wasted on plate adds to expense), wearing off occurring only up to the rivet head. Thus only 40% wears off, 60% is wasted. Further these clutches contain springs for smooth operation of clutch when gears are changed. Various remedies have been attempted to improve the performance of clutch, including silicon based applications. One of them is oriented towards compositions that can be used as adhesives which are replacement to the rivets used.

In general, epoxy based material are known for their excellent adhesion, chemical and heat resistance, good-to-excellent mechanical properties and very good electrical insulating properties. Epoxy adhesives are a major part of the class of adhesives called “structural adhesives” or “engineering adhesives”. These high-performance adhesives are used in the construction of aircraft, automobiles, bicycles, boats, golf clubs, skis, snowboards, and other applications where high strength bonds are required. Further, epoxy adhesives can be used as adhesives for wood, metal, glass, stone, and some plastics.

Two critical characteristics which determine the commercial use of adhesive is the shear strength and the peel strength. Standard epoxy resin compositions based on bisphenol-A and epichlorohydrin compounded with various thermally active latent hardener and optionally accelerators, fillers, thixotropic auxiliaries and the conventional additives are hard and brittle in the cured state. They exhibit very high tensile strength but on exposure to impact, peel stress, they flake leading to failure of the adhesive joints. References may be made to patent U.S. Pat. No. 6,645,341 discloses a two-component epoxy-based adhesive comprising a resin component and a curing agent where the resin component comprises an epoxy resin, a polymer polyol, and fumed silica. The curing agent comprises a polyoxyalkyleneamine, an amine terminated butadiene-acrylonitrile polymer, tris(2,4,6-dimethlaminomethyl)phenol, polyamide resin, silane and fumed silica. Further, Table 1 of said patent describes adhesives with various additives consisting of resin and curing agent in a molar ratio of 3:1 and Table 2 mentions that the ingredients of the curing agent portion of the adhesive described in Table 1 affect the lap shear strength and peel strength of the adhesive. However, said patent does not disclose the measurement of the lap shear strength of the adhesive composition at elevated temperature. The adhesive composition is useful for bonding of metals, plastics and composites and for functions such as laminating, honeycomb bonding, automotive assembly and construction assembly. References may be made to patent application US2011039108, relates to a heat-curable structural adhesive composition of high impact strength comprising one or more epoxy-resins of glycidyl ethers of bisphenol A, toughening agents, a curing agent capable of cross linking the epoxy resins and an acetoacetoxy-functionalized compounds.

Attempts have been made to toughen the epoxy resin based adhesives for low temperature applications. But adhesive compositions for clutch application have a requirement of high temperature stable epoxy resin composition coupled with a high lap shear strength i.e. bond strength while simultaneously balancing the required cushioning property. Very few compositions balance both these requirements; however, there is a gap in the art which can be filled by providing an improved adhesive composition that delivers improved lap shear strength without a compromise on its cushioning property. Moreover, a need is felt to provide a clutch disc adhesive composition such that it is worn off completely, thus making it an economically friendly option to mechanical rivets, soldering techniques for bonding, which retains such improved properties at higher temperatures.

WO 2008/089410 A1 discloses an epoxy resin composition comprising an epoxy resin, one or more toughening agents, a curing agent and acetoacetoxy-functionalized compounds. Whereas in the present application, one component epoxy adhesive comprising of an elastomer or a toughening agent and an additive is used. Further, acrylic polymers and butadiene nitrile rubbers are claimed as tougheners in WO 2008/089410 A1, whereas in the present application a hydrogenated carboxylated butadiene acrylonitrile rubber is a toughener. In WO 2008/089410 A1 carboxyl terminated butadiene nitrile (CTBN) rubbers are mixed with epoxy resins and their lap shear strength is measured as per ASTM D 1002 at room temperature whereas in the present application, the lap shear strength is measured as per ASTM D 2295-96 at elevated temperature.

US 2008/319105 A1 discloses a one component adhesive composition comprising one or more epoxy resins, at least one toughener rubber, a polytetrahydrofuran-based toughener that has isocyanate groups that are blocked or capped with a phenolic compound, an aminophenolic compound, a primary or secondary aliphatic or cycloaliphatic amine, an alalkyl alcohol, an aromatic amine, an alalkyl benzyl amine or an alkyl thiol; and one or more epoxy curing agents.

The adhesive composition in US 2008/319105 A1 is different from that described in the present application. The present application discloses adhesive composition comprising an epoxy resin, with elastomer or toughening agent such as partially hydrogenated carboxylated butadiene acrylonitrile rubber (HX-NBR) or additives.

The compositions of US 2008/319105 A1 are tested for their lap shear strength according to method DIN EN 1465 which is quite different as compared to present application. In the present application, the lap shear strength is measured at elevated temperature.

The application of the adhesive composition in US 2008/319105 A1 is as a structural adhesive to join the two metals, whereas, in the present application, the adhesive composition is used for bonding metal and non-metal parts in automotive clutches.

WO 2008/070825 A1 relates to a damping material based on a carbon containing nano-material, a curable matrix, and a block copolymer comprising a functional block and a non-functional block, a carbon containing nano-material is selected from the group consisting of a carbon nano-tube, a carbon nano-fibre, and group consisting of isoprene, styrene, and butadiene and the functional block is selected from the group consisting of 4-vinyl pyridine, N,N-(dimethylamino)ethyl methacrylate, methacrylic acid and acrylic acid.

The composition in WO 2008/070825 A1 contains hydrogenated nitrile butadiene polymers (HNBR), whereas the present composition contains a partially hydrogenated carboxylated acrylonitrile butadiene polymer (HXNBR). The application in the present application is also very different from that described in the WO 2008/070825 A1.

EP 1916272 A1 discloses the use of polyurethane material prepared from polyols and isocyanates whereas the present application does not use isocyanate, polyol or any polyurethane material prepared there from.

WO 2007/149377 A2 discloses an epoxy adhesive composition comprising components (A) and (B). Component (A) comprises at least one compound having average epoxy functionality, an epoxy-functionalized liquid rubber and component (B) comprises a curative comprising a polyamine, a flexible polyamide and, optionally an epoxy reactive liquid rubber. The epoxy adhesive composition upon curing has a lap shear strength of >1100 psi at 180° F. as measured by ASTM D 1002.

The present application discloses a one component epoxy adhesive composition comprising of epoxy resin, a toughening agent based on partially hydrogenated carboxylated nitrile butadiene rubber (HX-NBR) and additives. The lap shear strength is measured at elevated temperature at 150° C. in the present application. WO 2007/149377 A2 does not describe anything about the cushioning, whereas the present application describes the lap shear strength of 10-15 kg/cm² at 150° C. by retaining the desired cushioning.

EP 1832615 A2 discloses an epoxy adhesive composition comprising solid epoxies, latent hardeners, thixotropic agents and solvents. The solid epoxies are selected from the group consisting of epoxy functional butadiene, epoxy functional silicone, epoxy functional acrylic rubber, epoxy functional nitrile rubber, epoxy-CTBN adducts, epoxy urethane adducts and mixtures thereof. The document D6 does not claim anything about partially hydrogenated carboxylated butadiene acrylonitrile rubber (HX-NBR) which is used in the present application.

EP 0770656 A2 discloses an epoxy adhesive composition comprising a plateable adhesive for bonding cyanate ester composites together with a combination of a polymer mixture containing polyepoxide resin, a curing agent, and a filler containing a metal. The document EP 0770656 A2 also does not claim anything about partially hydrogenated carboxylated butadiene acrylonitrile rubber (HX-NBR) which is used in the present application.

U.S. Pat. No. 4,704,331 A discloses an adhesive composition comprising of an epoxy resin, curing agent polymeric toughening agent that has a rubbery phase and a thermoplastic phase, and a metal salt catalyst. The document D8 does not claim anything about partially hydrogenated carboxylated butadiene acrylonitrile rubber (HX-NBR) which is used in the present application.

WO 2011/056357 A1 discloses an adhesive composition comprising of an epoxy resin, isocyanate capped reactive elastomeric tougheners and a curing agent. WO 2011/056357 A1 does not claim anything about partially hydrogenated carboxylated butadiene acrylonitrile rubber (HX-NBR) which is used in the present application.

EP 2127865 A1 discloses an aluminium alloy composite comprising of a first metal part made of first aluminium alloy and an adherent part joined to the first metal part with an epoxy based adhesive. The epoxy based adhesive in EP 2127865 A1 contains 0 to 30 parts by weight of an elastomer component per 100 parts by weight of total resin components and a total of between 0 and 100 parts by weight of filler per 100 parts by weight of the total resin components. EP 2127865 A1 does not claim anything about partially hydrogenated carboxylated butadiene acrylonitrile rubber (HX-NBR) which is used in the present application.

OBJECTIVE OF THE INVENTION

Main objective of the present invention is to provide an adhesive composition.

Another objective of the present invention is to provide adhesive composition to obtain improved lap shear strength and cushioning property for clutch applications.

Yet another objective of the present invention is to provide adhesive composition comprising an epoxy resin in the range of 50-95 parts by weight and an elastomer in the range of 2 to 50 parts by weight and optionally a toughening agent in the range of 2-50 parts by weight and also optionally one or more additives in the range of 2-5 parts by weight.

SUMMARY OF THE INVENTION

Accordingly, present invention provides adhesive composition comprising an epoxy resin in the range of 5095 parts by weight and an elastomer in the range of 2 to 50 parts by weight and optionally a toughening agent in the range of 2-50 parts by weight and also optionally one or more additives in the range of 2-5 parts by weight.

In yet another embodiment of the present invention, epoxy resin used is Bisphenol A epoxy resin.

In yet another embodiment of the present invention, elastomers used are selected from the group consisting of amino terminated butadiene acrylonitrile co-polymer (ATBN), carboxyl terminated butadiene acrylonitrile co-polymer (CTBN), vinyl terminated butadiene acrylonitrile co-polymer (VTBN), epoxy terminated butadiene acrylonitrile co-polymer (ETBN), polyether, polyester, polyacrylates, silicone or hydroxyl terminated poly butadiene (HTPB).

In yet another embodiment of the present invention, toughening agents used are selected from carboxyl terminated butadiene nitrile rubbers, acrylic polymers, partially hydrogenated carboxylated nitrile butadiene rubber (HX-NBR) or hydrogenated Nitrile Butadiene Rubber (HNBR).

In yet another embodiment of the present invention, additives used are selected from the group consisting of diluents, fillers or pigments.

In yet another embodiment of the present invention, diluents used are selected from the group consisting of diglycidyl ether of resorcinol, diglycidyl ether of cyclohexane dimethanol, diglycidyl ether of neopentyl glycol or triglycidyl ether of trimethylolpropane.

In yet another embodiment of the present invention, filler used are selected from the group consisting of silica-gels, Ca-silicates, phosphates, molybdates, fumed silica, bentonite, wollastonite, organoclays, aluminium-trihydrates, hollow-glass-micro spheres, hollow-polymeric microspheres or calcium-carbonate.

In yet another embodiment of the present invention, pigments used are selected from the group consisting of ferric oxide, brick dust, carbon black or titanium oxide.

In yet another embodiment of the present invention, said composition has the lap shear strength in the range of 9 to 15 kg/cm² and cushioning effect is in the range of 0.4-0.6mm. In yet another embodiment of the present invention, said adhesive composition is stable at a temperature in the range of 25 to 160° C. without compromising the cushioning effect.

In yet another embodiment of the present invention, the composition is in liquid form or in paste form.

In yet another embodiment of the present invention, said composition has following characteristics:

-   -   a. Viscosity: 295,000 mPa.s     -   b. Specific gravity: 1.66     -   c. Lap shear strength: 322 kg/cm2     -   d. Tg (DSC): 118° C.     -   e. Cure conditions: @ 150° C. for more than 15 minutes.

In yet another embodiment of the present invention, one-pot process for the preparation of the adhesive composition comprising mixing compounded epoxy resin in the range of 50-90 parts by weight, elastomer in the range of 2 to 50 parts by weight, toughening agent in the range of 2-50 parts by weight, optionally with additives in the range of 2-5 parts by weight followed by mixing thoroughly and applied on the substrate previously treated with 2-5 parts by weight of coupling agent.

In yet another embodiment of the present invention, coupling agent used are selected from the group consisting of glycidyloxypropyl trialkoxy silane, mercaptopropyl trialkoxy silane or aminopropyl trialkoxy silane.

In yet another embodiment of the present invention, said composition provides improved lap shear strength and cushioning property for clutch applications.

In yet another embodiment of the present invention, adhesive composition is selected from a one-part or two part composition; preferably as a two part composition wherein one part adhesive system contain all the ingredients (base resin and elastomer) are in one pack whereas, in a two part adhesive system, the resin and the toughening agents are mixed just before the application.

In yet another embodiment of the present invention, a one-pot process for the preparation of the adhesive composition comprising mixing compounded epoxy resin with toughening agent in the ratio 80:20 followed by mixing thoroughly and applied on the substrate previously treated with silane coupling agent.

DETAILED DESCRIPTION OF INVENTION

In an aspect the present invention relates to adhesive composition comprising of Henkel adhesive, an elastomer such as CTBN or ATBN optionally with a coupling agent and additives. In a preferred aspect, the current invention provides an adhesive composition comprising of an epoxy resin basically of bisphenol A and epichlorohydrin; and partially hydrogenated carboxylated nitrile butadiene rubber (HX-NBR) in solid form as a toughening agent in the ratio 80:20 optionally with additives to obtain improved lap shear strength and cushioning properties.

The adhesive composition of the instant invention is stable at high temperature and has improved lap shear strength that can withstand temperature upto 160° C. without compromising the cushioning effect.

The present invention provides high temperature resistant epoxy based adhesive composition consisting of an epoxy resin component, elastomer, toughening agent, a coupling agent, optionally with additives such as diluents, fillers, pigments to obtain improved lap shear strength and cushioning properties for clutch disc application.

Examples of epoxy resin suitable for use in the present invention include HPA 1044 of Henkel; or polyepoxides formed by reacting epichlorohydrin with 4, 4 isopropylidene diphenol and having a molecular weight ranging from about 340 to about 10,000. Most preferably, the polyepoxides have a molecular weight range from about 330 to 560 and contain at least two oxirane groups; i.e., two epoxy groups; or include monofunctional and multifunctional glycidyl ethers of bisphenol A and bisphenol F, and cycloaliphatic epoxy resins or a combination thereof. The cycloaliphatic epoxides are preferably selected from non-glycidyl ether epoxides containing more than one 1.2 epoxy group per molecule such as 3,4-epoxycyclohexylmethyl-3,4 -epoxycyclohexane carboxylate, which contains two epoxide groups that are part of the ring structures and an ester linkage, vinylcyclohexene dioxide, which contains two epoxide groups and one of which is part of the ring structure, 3,4-epoxy-6-methyl cyclohexyl methyl-3,4-epoxycyclohexane carboxylate and dicyclopentadiene dioxide. Glycidyl ether epoxides are used either separately or in combination with the non-glycidyl ether epoxides. These resins are selected from glycidyl ether epoxides containing more than one 1.2 epoxy group per molecule. A preferred epoxy resin of this type is Bisphenol A resin which includes 2,2-bis(4-hydroxyphenyl) propane-epichlorohydrin copolymer. These resins are generally prepared by the reaction of one mole of bisphenol A resin and two moles of epichlorohydrin. The preferred epoxy for the adhesive of the present invention is selected from HPA 1044 of Henkel or Bisphenol A resin. Bisphenol-A type resin is commercially available from Resolution Technology a., EPON 828, 828EL or 828XA. The epoxy resin component of the resin comprises from about 50 to about 90 weight percent of the resin component and, preferably, about 75 to about 85 weight percent of the resin component.

The elastomers of the present invention are selected from butadiene acrylonitrile copolymers namely amino terminated butadiene acrylonitrile co-polymer (ATBN), carboxyl terminated butadiene acrylonitrile co-polymer (CTBN), vinyl terminated butadiene acrylonitrile co-polymer (VTBN), epoxy terminated butadiene acrylonitrile co-polymer (ETBN), polyether, polyester, polyacrylates, silicone, hydroxyl terminated poly butadiene (HTPB) and such like. The adhesive composition comprises silane coupling agents, selected from, but not limited to glycidyloxypropyl trialkoxy silane, mercaptopropyl trialkoxy silane, aminopropyl trialkoxy silane, and such like. In addition, organo-silanes may contain moieties, such as, for example, ester, vinyl, methacryloxy, sulfur, amino, ureido, isocyanurate, and isocyanato groups.

The toughening agents are primarily the polymers other than epoxy resins capable of increasing the toughness of the epoxy resin. The toughness is measured by the peel strength of the eoxy resin. Typical toughening agents are selected from carboxyl terminated butadiene nitrile rubbers, acrylic polymers and copolymers etc. However, the unsaturated polymers have low resistance to heat, water, and impact. To withstand the high temperature and high peel strength, the toughening agents in the present invention is selected from partially hydrogenated carboxylated butadiene nitrile rubbers in the range of 20 wt %.

Hydrogenated Nitrile Butadiene Rubber (HNBR) is a special class of nitrile rubber (NBR) that is hydrogenated to increase saturation of the butadiene segment of the carbon polymer backbone. Substantial improvements to the material properties, over that of a nitrile rubber (NBR), include greater thermal stability, broader chemical resistance, and greater tensile strength. Moreover, addition of carboxylic acid groups to the NBR polymer's backbone significantly alters processing and cured properties. It also results is a polymer matrix with significantly increased strength, measured by improved tensile, tear, modulus and abrasion resistance.

Present invention provides an adhesive composition comprising of HPA 1044 of Henkel and an elastomer CTBN or ATBN optionally with a coupling agent and additives having following specifications;

a. Viscosity: 295,000 mPa.s

b. Specific gravity: 1.66

c. Lap shear strength: 322 kg/cm2

d. Tg (DSC): 118° C.

e. Cure conditions: @ 150° C. for more than 15 minutes

The epoxy resin in the adhesive composition of the invention is in the range of 50-90 parts by weight and elastomer is in the range of 2-50 parts by weight. The coupling agent is in the range of 2-5% parts by weight of the adhesive composition.

The present invention provides an adhesive composition for clutch disc application comprising of an epoxy resin basically of bisphenol A and epichlorohydrin; and partially hydrogenated carboxylated nitrile butadiene rubber (HX-NBR) in solid form as a toughening agent in the ratio 80:20 optionally with additives with improved lap shear strength and cushioning properties.

The epoxy resin is in the range of 50-90 parts by weight and the toughening agent in the range of 2-50 parts by weight optionally with additives in the range of 2-5 parts by weight The adhesive composition of the instant invention is stable at a temperature in the range of 25° C. to 160° C. and has a lap shear strength not less than 10 kg/cm² with an average cushioning of 0.4-0.6 mm.

The diluent may be added to the adhesive composition to control the flow characteristics and is selected from diglycidyl ether of resorcinol, diglycidyl ether of cyclohexane dimethanol, diglycidyl ether of neopentyl glycol, triglycidyl ether of trimethylolpropane.

Fillers may include adhesion promoters, corrosion inhibitors and rheology controlling agents and may be selected from silica-gels, Ca-silicates, phosphates, molybdates, fumed silica, clays such as bentonite or wollastonite, organoclays, aluminium-trihydrates, hollow-glass-micro spheres; hollow-polymeric microspheres and calcium-carbonate.

Pigments may include inorganic or organic pigments including ferric oxide, brick dust, carbon black, titanium oxide and the like.

The adhesive composition of the instant invention may be a one-part or two part composition; preferably as a two part composition.

The invention provides a one-pot process for the preparation of the adhesive composition comprising mixing compounded epoxy resin with toughening agent in the ratio 80:20. The contents are mixed thoroughly and applied on the substrate previously treated with silane coupling agent.

The physical properties of HPA 1044 (Henkel Adhesives) used in the present invention are given in Table 1 below:

TABLE 1 Properties Observation Appearance Brownish Grey Paste Viscosity Brookfield RV #7@10 rpm 295,000 mPa · s HAAKE Viscosity (RS-1, CS35/2-Ti) 97,000 mPa · s @ 20 s⁻¹ HAAKE Viscosity (RS-1, CS35/2-Ti) 2.23 Thixo ratio (2 s⁻¹/20 s⁻¹) Specific Gravity 1.66 Lap Shear Strength (GB Steel, 0 gap@ 32.2 N/mm² 150° C. × 30 min) Tg (DSC) 118° C.

The adhesive of the present invention can be applied as liquid, paste, and semi-solid or solid that can be liquefied upon heating, or the adhesive may be applied as a spray. It can be applied as a continuous bead, in intermediate dots, stripes, diagonals or any other geometrical form that will conform to forming a useful bond. Preferably, the adhesive composition is in a liquid or paste form. The composition may be used as a metal-metal adhesive, metal-carbon fiber adhesive, carbon fiber-carbon fiber adhesive, metal⁻glass adhesive, carbon fiber-glass adhesive.

The adhesive composition of the present invention contains low amount of volatile organic compounds thus providing an environment friendly, economical option for the mechanical rivet. Such compositions of the invention find use in clutch disc applications.

EXAMPLE

Following examples are given by way of illustration therefore should not be construed to limit the scope of the present invention in any manner.

Example 1

Ingredients Parts by weight HPA-1044 95 CTBN (elastomer) 5

APTES (Aminopropyl triethoxy silane) is used as coupling agent.

Example 2

Ingredients Parts by weight HPA-1044 85 ATBN 15

APTES (Aminopropyl triethoxy silane) is used as coupling agent.

Example 3

ingredients Parts by weight HPA-1044 80 HXNBR 20

MEK (Methyl ethyl ketone) is used to dissolve these ingredients.

APTES (Aminopropyl triethoxy silane) is used as coupling agent.

Test for Lap Shear Strength and Cushioning

The lap shear strength (LSS) test specimens were prepared as per the ASTM D1002. For this the test specimens in the form of strips of dimension 100 mm in length and 25 mm in width were prepared from mild steel (1.6 mm thick) and organo-metallic friction material (4.2 mm thick). Test specimens, were cleaned to remove oil, dust and grease materials from the surface. Amino functional silane was applied over the cleaned surface in an area of one inch by half inch. An adhesive composition was prepared by mixing the ingredients as given herein. Silane coated test specimens were bonded together with this adhesive and cured at 150° C. for 90 minutes. Testing was done at 150° C. after seven days of post curing at 27° C.

Test Results for Lap Shear Strength and Cushioning

I) Measurement of Lap Shear Strength

The strips bonded with adhesive were evaluated at 27° C. and at 150 ° C. for lap shear strength using a Universal tensile tester (Instron) as per procedure in ASTM D 1002⁻05.

II) Measurement of Cushioning Property

The adhesive bonded test specimen was kept in between two stainless steel plates and a load of 10 kg/cm² was applied. The gap between the plates was measured before and after the application of the load. From this the cushion parameters were calculated.

TABLE 2 Test results for lap shear strength and cushioning LSS (kg/cm²) @ 150° C. Cushioning (mm) Example 1 15 0.08 Example 2 9.5 0.15 Example 3 11 0.5

1) Substrates used for evaluating the bond strength of the adhesive composition of the present invention are mild steel, concrete, friction facings and ceramics.

-   -   Metal (mild steel)

The LSS of the present adhesive composition using mild steel as the substrate at room temperature was 120 kg/cm² and 25 kg/cm² at 150° C.

-   -   Concrete

Concrete substrates were not used in the present invention

-   -   Friction facing

The LSS of the present adhesive composition using friction facing as the substrate was 17.6 kg/cm² at 150° C.

-   -   Ceramics

The LSS of the present adhesive composition using ceramics as the substrate was 15 kg/cm² at 180° C.

2) Elastic behavior

FIGS. 1 and 2 show the temperature dependent viscoelastic properties (storage modulus, E′ and tan δ) of epoxy adhesive formulations with varying amounts of ATBN content (unmodified, 10%, 15% and 20%). It can be readily seen from the FIG. 1 that with an increase in ATBN content, there is a monotonic decrease in the storage modulus, E′. The tan δ curves of epoxy adhesive formulations with increasing ATBN content shown in FIG. 2 clearly indicate the decrease in T_(g) values (obtained from peak positions) from 135° C. (unmodified) to 123° C. (for the 20% ATBN content). Both the results unequivocally confirm the increased elasticity of the adhesive formulations.

3) Cycles

TABLE 1 330 Dia Clutch Sub assembly with adhesive composition containing HPA 1044 & ATBN (20%) Disc 1 After Testing at Sl. Before 5000 No. Description Testing cycles Remarks Disc 2 1. Avg. free 9.74 9.62 Initial cushioning 9.76 thickness observed in 3 places upto 0.36 to 0.38 which is nearer to the Spec. After 5000 cycles, Cushioning drop observed 19.4%. 2. Avg. thickness 9.38 9.32 9.38 under load at 800 kg 3. Avg. 0.36 0.29 0.38 cushioning at 800 kg Load

As shown in Table-1, in case of 310 dia clutch sub assembly, the free thickness variation observed was upto 1.02 mm, but the cushioning observed was more as compared to 280 dia clutch sub assembly. The composition containing HPA1044 and ATBN 20% has shown initial cushioning in 3 places upto 0.36 to 0.38 which is nearer to the specification. After 5000 cycles, the cushioning drop observed was 19.4%.

TABLE 2 Results for the 280 mm dia clutch discs with the combination of adhesive and metal cushion springs (Adhesive composition: HPA1044 + 20% ATBN) Cushioning (0.50-0.80 mm) at 850 kg Load Sample No. I II III I 0.33 0.66 0.36 II 0.40 0.70 0.58 III 0.30 0.65 0.50 IV 0.43 0.41 0.40 V 0.50 0.87 0.82 VI 0.56 0.85 0.69

It can be seen from Table-2 that, the average value of cushioning obtained under the load of 850 Kg is in the desired range of 0.5-0.8 mm.

4) Temperature range 25-150° C.

The adhesive composition of the present invention has been evaluated for LSS at room temperature (25° C.) and at 150° C. The data is already mentioned in (1) above.

5) Adhesive strength

At normal condition

The adhesive strength when tested at 150° C. without prolonged heating was 17.6 kg/cm².

After 10,000 cycles at 150° C., the composition has retained the minimum adhesive strength of 10 kg/cm².

TABLE 3 LSS of HPA1044 + 20% ATBN adhesive composition tested at 150° C. for different durations Heat ageing @ 150° C. Average Lap Shear Strength Sr. No. (Hours) (kg/cm²) 1. 0 8.15 2. 15 7.19 3. 30 7.61

It can be readily seen from Table-3 that the prolonged heating does not alter the adhesive strength of the adhesively bonded specimens to a great extent.

Advantages of the Invention

1. Adhesively bonded clutch disc provide 100% utilization of the friction material.

2. There is no loss of friction material.

3. Life time of clutch disc is increased.

4. There is a reduction in the overall weight of clutch disc.

5. The process for the preparation of adhesively bonded clutch disc is easier and economical. 

1. Adhesive composition comprising an epoxy resin in the range of 50-95 parts by weight and an elastomer in the range of 2 to 50 parts by weight and optionally a toughening agent in the range of 2-50 parts by weight and also optionally one or more additives in the range of 2-5 parts by weight.
 2. The adhesive composition as claimed in claim 1, wherein epoxy resin used is Bisphenol A epoxy resin.
 3. The adhesive composition as claimed in claim 1, wherein elastomers used are selected from the group consisting of amino terminated butadiene acrylonitrile co-polymer (ATBN), carboxyl terminated butadiene acrylonitrile co-polymer (CTBN), vinyl terminated butadiene acrylonitrile co-polymer (VTBN), epoxy terminated butadiene acrylonitrile co-polymer (ETBN), polyether, polyester, polyacrylates, silicone or hydroxyl terminated poly butadiene (HTPB).
 4. The adhesive composition as claimed in claim 1, wherein toughening agents used are selected from carboxyl terminated butadiene nitrile rubbers, acrylic polymers, partially hydrogenated carboxylated nitrile butadiene rubber (HX-NBR) or hydrogenated Nitrile Butadiene Rubber (HNBR).
 5. The adhesive composition as claimed in claim 1, wherein additives used are selected from the group consisting of diluents, fillers or pigments.
 6. The adhesive composition as claimed in claim 5, wherein diluents used are selected from the group consisting of diglycidyl ether of resorcinol, diglycidyl ether of cyclohexane dimethanol, diglycidyl ether of neopentyl glycol or triglycidyl ether of trimethylolpropane.
 7. The adhesive composition as claimed in claim 5, wherein filler used are selected from the group consisting of silica-gels, Ca-silicates, phosphates, molybdates, fumed silica, bentonite, wollastonite, organoclays, aluminium-trihydrates, hollow-glass-micro spheres, hollow-polymeric microspheres or calcium-carbonate.
 8. The adhesive composition as claimed in claim 5, wherein pigments used are selected from the group consisting of ferric oxide, brick dust, carbon black or titanium oxide.
 9. The adhesive composition according to claim 1, wherein said composition has the lap shear strength in the range of 9 to 15 kg/cm² and cushioning effect is in the range of 0.4-0.6mm.
 10. The adhesive composition according to claim 1, wherein said adhesive composition is stable at a temperature in the range of 25 to 160° C. without compromising the cushioning effect.
 11. The adhesive composition according to claim 1, wherein the composition is in liquid form or in paste form.
 12. The adhesive composition as claimed in claim 1, wherein said composition has following characteristics: a. Viscosity: 295,000 mPa.s b. Specific gravity: 1.66 c. Lap shear strength: 322 kg/cm2 d. Tg (DSC): 118° C. e. Cure conditions: @ 150° C. for more than 15 minutes.
 13. One-pot process for the preparation of the adhesive composition comprising mixing compounded epoxy resin in the range of 50-90 parts by weight, elastomer in the range of 2 to 50 parts by weight, toughening agent in the range of 2-50 parts by weight, optionally with additives in the range of 2-5 parts by weight followed by mixing thoroughly and applied on the substrate previously treated with 2-5 parts by weight of coupling agent selected from the group consisting of glycidyloxypropyl trialkoxy silane, mercaptopropyl trialkoxy silane or aminopropyl trialkoxy silane.
 14. The adhesive composition according to claim 1, wherein said composition provides improved lap shear strength and cushioning property for clutch applications. 